The present invention relates generally to a mechanical device that efficiently measures physical parameters such as compression strength, elasticity, firmness, deformation resistance and the like, on one or a plurality of compressible objects including fruits, nuts and vegetables and which operates in a semi-automatic fashion using an indexable turntable linked to one or a plurality of test stations capable of independently measuring said physical parameters.
More specifically, the present invention also relates to a mechanical device that employs at least one controlled free-fall test station to measure at least one of said physical parameters of a compressible object and which operates in a semi-automatic fashion using an indexable turntable to advance and test single or multiple sets of objects simultaneously using one or a plurality of test stations capable of independently measuring said physical parameters.
Various devices exist in the market to assist in testing physical properties of objects relating to the object's firmness, strength, compression resistance, elasticity and recovery from deformation, such as firmometers, penetrometers, impact testers and compression testers. Examples of firmometers and penetrometers include the Magness-Taylor pressure tester (devised in 1925) and the Effegi tester (developed recently in Italy) which make acceptance measurements but are mainly used owing to the convenience of portability due to their handheld configurations and compact size. (J. Amer. Soc. Hort. Sci. 101(6):698-700. 1976.)
Benchtop testing devices include the Instron Universal Testing Machine (available from Instron, 825 University Ave., Norwood, Mass. 02062-2643) and the Anderson firmometer (as described in the “Proceedings from the Joint Conference of the Australian Avocado Grower's Federation, Inc. and NZ Avocado Growers Association, Inc.,” on 23-26 Sep. 1997. J. G. Cutting (Editor) Pages 69-75).
For certain fruit, such as cherries, testing devices have been specifically designed, such as the FirmTech1 (available from BioWorks, Inc., 31480 Hwy. K-18, Wamego, Kans. 66547, U.S.A.) The FirmTech1 device measures firmness using a force deformation mode of action. Cherries are positioned into shallow indentures on a turntable which automatically rotates to align each cherry periodically under a small load cell. A pre-determined force is progressively applied onto the cherry and the response measured by the load cell. The rate at which the force increases is defined as firmness. For a sample of cherries, average firmness, sample maximum and minimum firmness, sample standard deviation of firmness, and a frequency distribution of firmness are presented through an interfaced computer. Firmness of individual cherries in the sample can be retrieved from a file accessed through the computer. (see “Evaluation of Four Cherry Firmness Measuring Devices”, Authors: Elizabeth Mitcham, Murray Clayton, Bill Biasi, and Steve Southwick, Department of Pomology, University of California, Davis, Calif. 95616, 13th Annual Postharvest Conference March 1997.) A similar device is the Soft Fruits Laboratory Turntable Firmometer available from Agrosta Sarl, 13 Rue du Bastringue 76440 Serquex, France.
However, both the Agrosta instrument and the FirmTech 1, operates by applying a progressively increasing and pre-determined force applied by use of a linear actuator or a stepper motor, which both operate by means of incremental steps produced by an electronic control module that operates to electrically pulse the actuators to advance them one step per pulse, typically a small linear distance or small rotational movement, such that a large number of pulses are typically required to move an appreciable distance. Accordingly, the applied force from these motors is produced by a series of short, fast and discreet incremental steps, which then acts to apply force to the test object or fruit piece as a series of discreet incremental force increases, which is the equivalent of a series of discreet impact events. In other words, the force applied by these current instruments is essentially equivalent to an increasing ratchet-like force, increasing incrementally in a manner that is neither smooth nor continuous in nature. Thus, any concurrent compression readings obtained from a load cell, transducer or other sensor that is being driven by a linear actuator or stepper motor necessarily suffers from the superposition of the applied, discreet increments of force applied to the object and the object's concurrent, reactive impulse to resist deformation, causing a matching series of responsive rebounds to each successive incremental pulse. Accordingly, the present means to apply force acts to introduce transient artifacts into the data stream collected during a sampling event using a stepper driven load cell to record compression and deformation resistance.
While this issue can be partially addressed by selecting linear actuators and stepper motors with high resolution capability (high number of steps per linear displacement or angular degree), the motors still operate in the same manner, so that the distortion effect is only decreased, but not eliminated. Further, the cost and size of the higher resolution motors and the electronic control modules to run them quickly become prohibitive compared to the cost of manual firmometers where one applies the force by hand or semi-automatic firmometers where force is applied using a lever.
Accordingly, what would be highly desirable is a device with means to apply a steady, continuous force during the compression test cycle rather than a series of incremental pulsed displacements, so that the collected data from a load cell, transducer or other pressure or force sensitive sensor is of much higher quality and not superimposed or contaminated with artifacts caused by the applied pulses and rebounds resulting from a stepped force application approach.
What is also desired is a device that can simultaneously measure a plurality of test objects or fruit pieces simultaneously, enabling multiple fruit pieces to be tested together. What is also desired is a device that can simultaneously measure a control object and a fruit piece to be tested together, or a first and second test of a single test object or fruit piece, and similar combinations, to be conducted either simultaneously or sequentially to calibrate the measurement systems of the device, compare calibration between the measurement systems, and to enable calibration of test measurement results obtained from testing of a control object or a fruit piece.
What is also desired is a device that does not require the use of either linear or rotational stepper motors or controllers in the mechanism of the measurement systems where they are used to directly apply force to a fruit piece or test object.